1. Field of the Invention
This invention relates to a method and apparatus for a printed wiring board for forming a protective water-soluble pre-flux film on the surface of a conductor pattern facing outwards.
2. Description of Related Art
In a printed wiring board, a pre-flux film is routinely formed on its conductor pattern following the formation of the conductor pattern and prior to ultimate inspection such as substrate appearance inspection. For forming this pre-flux film, a solvent type pre-flux or a water-soluble pre-flux is used.
Meanwhile, since the solvent type pre-flux, which enables quality stability for the pre-flux film due to its high adhesion to a conductor pattern to assure stabilized film forming and also due to its superior solder wettability, is prepared using a large quantity of the volatile organic compounds (VOCs), the tendency is to use the solvent type pre-flux only in a limited quantity in view of environmental protection.
On the other hand, in a water-soluble pre-flux, not employing the VOCs, sufficient quality stability cannot be realized as compared to the solvent type pre-flux. For example, the water-soluble pre-flux is inferior to the solvent type pre-flux in adhesion to the conductor pattern, such that stable pre-flux films cannot be formed. In addition, the water-soluble pre-flux liquid is inferior in solder wettability.
It is therefore an object of the present invention to provide a method and apparatus for surface treatment of a printed wiring board capable of forming a pre-flux film of stable quality on a conductor pattern using a water-soluble pre-flux.
In one aspect, the present invention provides a surface-processing apparatus for a printed wiring board including means for etching the surface of a conductor pattern formed on at least one surface of a printed wiring board, first rinsing means for rinsing the surface of the printed wiring board the conductor pattern of which has been etched by the etching means, air bubble removing means for removing air bubbles affixed to the surface of the printed wiring board by immersing the printed wiring board rinsed by the first rinsing means in a water-soluble pre-flux liquid in a processing vessel, pre-flux forming means for forming a pre-flux film on the conductor pattern on the printed wiring board in the pre-flux liquid, freed of air bubbles by the air bubble removing means, using an in-liquid spray provided in the pre-flux liquid in the processing vessel, liquid removing means for removing the pre-flux liquid from the surface of the printed wiring board carrying the pre-flux film and second rinsing means for rinsing the surface of the printed wiring board from the surface of which the pre-flux liquid has been removed by the liquid removing means.
In another aspect, the present invention provides a surface-processing method for a printed wiring board including the steps of etching the surface of a conductor pattern formed on at least one surface of a printed wiring board, rinsing the surface of the printed wiring board the conductor pattern of which has been etched by the etching step, removing air bubbles affixed to the surface of the printed wiring board by immersing the printed wiring board rinsed by the first rinsing step in a water-soluble pre-flux liquid in a processing vessel, forming a pre-flux film on the conductor pattern on the printed wiring board in the pre-flux liquid, freed of air bubbles, using an in-liquid spray provided in the pre-flux liquid in the processing vessel, removing the pre-flux liquid from the surface of the printed wiring board carrying the pre-flux film and transferred from the processing vessel, and rinsing the surface of the printed wiring board from the surface of which the pre-flux liquid has been removed by the liquid removing step.
According to the present invention, the conductor patterns on the printed wiring board are etched to remove surface oxides to provide for a planar surface. The liquid etchant then is rinsed off to form a pre-flux film. So, the pre-flux film may be improved in adhesion, while the pre-flux film is not affected by the surface oxides on the conductor patterns and hence may be a smooth surface. The pre-flux film is formed using an in-liquid spraying unit, so that it may be of uniform film thickness, while solder wettability is also improved.